The present invention relates to a canister to be used in the fuel supplying system of an internal combustion engine of a vehicle.
Generally, the canister is provided with a housing accomodating a bed of an adsorbent material. In an upper end wall of the housing, a fuel vapors inlet port communicated with a fuel source, and a purged vapors outlet port communicated with an intake passage of the internal combustion engine are provided. And in a lower end wall which is opposed to the upper end wall through the bed of adsorbent material, an air suction port communicated with the atmosphere, is provided.
When the internal combustion engine is stopped, the fuel vapors entering the housing from the fuel vapors inlet port, flow into the bed from the upper surface thereof and are adsorbed by the adsorbent material.
When the engine is in operation, negative pressure is generated in the intake passage so that fresh air is sucked into the bed of adsorbent material from the air suction port. Consequently, the fuel vapors which are adsorbed by the adsorbent material, are purged therefrom, and the purged vapors are sucked into the intake passage.
The conventional canister of this type has a problem as follows. Namely, during hot weather periods, fuel vapors are apt to be supplied into the housing in the fuel vapor purging process. The introduced fuel vapors are directly sucked from the housing through the purged vapors outlet port without flowing into the bed of adsorbent material so that air-fuel ratio temporarily decreases so as to lower the engine performance and increase the amount of unburnt components in exhaust gases.
In order to solve the above problem, a fuel vapors guiding pipe of which base end is communicated with the fuel vapors inlet port and which projects into the adsorbent bed has been employed. By providing the fuel vapors guiding pipe, the fuel vapors are guided into the absorbent bed that the fuel vapors can be prevented from bypassing from the fuel vapors inlet port to the purged vapors outlet port without passing through the adsorbent bed.
However, the canister provided with the fuel vapors guiding pipe has such a problem that the fuel vapors cannot reach the upper portion of the adsorbent bed above the projecting end of the guiding pipe, and that the fuel vapors cannot reach the outer peripheral portion of the adsorbent bed since the guiding pipe has a diameter considerably smaller than that of the housing. As a result, the adsorbing efficiency of the adsorbent bed is lowered.
In order to solve the above problem, a frusto-conical deflector has been employed. In this case, the deflector is buried within the adsorbent bed so as to be opposed to the projecting end of the fuel vapors guiding pipe for deflecting the flow of the fuel vapors guided by the fuel vapors guiding pipe in the direction of the upper portion and the outer peripheral portion of the bed.
By providing the deflector in the canister, adsorbing capacity of bed is improved but the flow of the sucked air is obstructed by the deflector so that the amount of unpurged fuel vapors is large.
Accordingly, an object of the present invention is to provide a canister having excellent adsorbing and purging capacity.
Another object of the present invention is to provide a canister having a deflector which guides the fuel vapors flowing into a bed of adsorbent material so as to be dispersed throughout the whole bed and does not obstruct the flow of fresh air sucked into the bed.